Thanks. I’m paraphrasing the explanation from a book called “Why does E=MC2?” By Dr. Brian Cox and Dr. Jeff Forshaw. The book is written to explain the theory of relativity in a way normal people can understand, and talks about the implications of that theory on the real world. Makes a hard topic easy and fun to understand, so if you are interested I highly recommend it.

It does apply to earth. All motion is relative to something else. How fast are you going right now? You may be sitting still and think, I’m not moving at all. Ok, but the earth is spinning, so now how fast are you going? Ok, but the earth is also rotating around the sun. It’s also part of the solar system, which is moving, but it’s also part of the Milky Way, which is moving. But it also is part of the universe, which is expanding. So how fast are you going? The only way to answer it is to measure your speed “relative” to another object

Was it pizza by Alfredo or Alfredo’s pizza kitchen?